US8288475B2 - Process for producing electret, and electrostatic induction conversion device - Google Patents

Process for producing electret, and electrostatic induction conversion device Download PDF

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US8288475B2
US8288475B2 US13/177,493 US201113177493A US8288475B2 US 8288475 B2 US8288475 B2 US 8288475B2 US 201113177493 A US201113177493 A US 201113177493A US 8288475 B2 US8288475 B2 US 8288475B2
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polymer
fluorinated
group
electret
silane coupling
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US20110263788A1 (en
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Kimiaki Kashiwagi
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AGC Inc
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Asahi Glass Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G7/00—Capacitors in which the capacitance is varied by non-mechanical means; Processes of their manufacture
    • H01G7/02—Electrets, i.e. having a permanently-polarised dielectric
    • H01G7/021—Electrets, i.e. having a permanently-polarised dielectric having an organic dielectric
    • H01G7/023—Electrets, i.e. having a permanently-polarised dielectric having an organic dielectric of macromolecular compounds
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G7/00—Capacitors in which the capacitance is varied by non-mechanical means; Processes of their manufacture
    • H01G7/02—Electrets, i.e. having a permanently-polarised dielectric
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G7/00—Capacitors in which the capacitance is varied by non-mechanical means; Processes of their manufacture
    • H01G7/02—Electrets, i.e. having a permanently-polarised dielectric
    • H01G7/028—Electrets, i.e. having a permanently-polarised dielectric having a heterogeneous dielectric
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
    • H04R19/00—Electrostatic transducers
    • H04R19/01—Electrostatic transducers characterised by the use of electrets
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
    • H04R19/00—Electrostatic transducers
    • H04R19/04—Microphones

Definitions

  • the present invention relates to a process for producing an electret, and an electrostatic induction conversion device.
  • an electrostatic induction conversion device such as a power-generating unit or a microphone
  • an electret having an electric charge injected to an insulating material is used.
  • Patent Document 1 discloses an Example wherein a polymer having an intrinsic viscosity of 0.23 (corresponding to a weight average molecular weight of 165,000) and a silane coupling agent are mixed and thermally treated at 200° C.
  • Patent Document 1 JP-A-2006-180450
  • Patent Document 2 WO2008/114489
  • An electret is required to have thermal stability in various applications.
  • ECM electret condenser microphone
  • injected electric charges are required to be maintained to some extent after a solder reflow step.
  • the maximum temperature of the solder reflow step is about 260° C., and in order to maintain a sufficient performance as ECM, it is important that the surface voltage after the step remains to be at least 200 V. The higher the remaining voltage, the higher the performance of ECM.
  • the present invention has been made in view of the above problem and has an object to provide a process for producing an electret which has high thermal stability of retained electric charge and which has excellent charge retention performance, and an electrostatic induction conversion device comprising such an electret.
  • the present invention provides the following.
  • a process for producing an electret which comprises a step of thermally treating a composition comprising a fluorinated polymer and a silane coupling agent, wherein the fluorinated polymer has an alicyclic structure in its main chain and has a carboxy group or an alkoxycarbonyl group as its terminal group; the silane coupling agent has an amino group; and the temperature for the thermal treatment is from 250° C. to 330° C.
  • silane coupling agent is at least one member selected from the group consisting of ⁇ -aminopropylmethyldiethoxysilane, ⁇ -aminopropylmethyldimethoxysilane, N-( ⁇ -aminoethyl)- ⁇ -aminopropylmethyldimethoxysilane, N-( ⁇ -aminoethyl)- ⁇ -aminopropylmethyldiethoxysilane, ⁇ -aminopropyltrimethoxysilane, ⁇ -aminopropyltriethoxysilane, N-( ⁇ -aminoethyl)- ⁇ -aminopropyltrimethoxysilane, N-( ⁇ -aminoethyl)- ⁇ -aminopropyltriethoxysilane and aminophenyltrimethoxysilane.
  • An electrostatic induction conversion device comprising the electret obtained by the process as defined in any one of [1] to [9].
  • an electret which has high stability with time and thermal stability of retained electric charge and which has excellent charge retention performance, and an electrostatic induction conversion device comprising such an electret.
  • FIG. 1 is a schematic diagram illustrating a corona charging equipment used for injection of electric charge.
  • FIG. 2 is a diagram showing set positions for measuring points for surface voltages.
  • FIG. 3 is a schematic diagram illustrating an equipment used for a thermal stability test.
  • FIG. 4 is shows standardized values of peak areas of infrared absorption spectra obtained in Test Example 4.
  • FIG. 5 is a scattering spectrum graph showing a result of measuring small-angle X-ray scattering of a coating film.
  • repeating units constituting a polymer may be referred to simply as “units”.
  • a compound represented by the formula (1) may be referred to also as “a compound (1)”.
  • a unit, compound or the like represented by another formula will be referred to in a similar manner, and for example, a unit represented by the formula (3-1) may be referred to also as “a unit (3-1)”.
  • the present invention is characterized by comprising a step of thermally treating a composition for an electret comprising a specific fluorinated polymer and a silane coupling agent at a specific temperature.
  • the present invention preferably includes the following steps in the following order.
  • a step of obtaining a coating fluid having the specific fluorinated polymer and the silane coupling agent dissolved in a solvent (a coating fluid-preparation step),
  • the specific fluorinated polymer (hereinafter referred to as the polymer (A)) to be used in the present invention is a fluorinated polymer having an alicyclic structure in its main chain and having a carboxy group or an alkoxycarbonyl group as its terminal group.
  • alicyclic structure means a cyclic structure having no aromaticity. Further, “having an alicyclic structure in its main chain” means that among carbon atoms constituting the cyclic structure, at least one is a carbon atom constituting the main chain of the polymer (A).
  • the alicyclic structure may be one wherein the cyclic skeleton is constituted solely by carbon atoms, or may be a heterocyclic structure which contains, in addition to carbon atoms, a heteroatom such as an oxygen atom, a nitrogen atom or the like.
  • a saturated or unsaturated hydrocarbon ring structure which may have a substituent, or a heterocyclic structure having some of carbon atoms in such a hydrocarbon ring structure substituted by a heteroatom such as oxygen atom, a nitrogen atom or the like, may be mentioned.
  • an alicyclic structure of a heterocyclic structure having 1 or 2 etheric oxygen atoms in its cyclic skeleton is preferred.
  • the number of atoms constituting the cyclic skeleton of the alicyclic structure is preferably from 4 to 7, more preferably 5 or 6. That is, the alicyclic structure is preferably a 4- to 7-membered ring, more preferably a 5- or 6-membered ring.
  • the carbon atoms constituting the main chain are derived from a polymerizable double bond of a monomer used for the polymerization for the polymer (A).
  • the fluorinated polymer is a fluorinated polymer obtained by polymerization of a cyclic monomer as described hereinafter, two carbon atoms constituting such a double bond become the carbon atoms constituting the main chain.
  • the polymer (A) is preferably a fluorinated polymer having a fluorinated alicyclic structure in its main chain. That is, the alicyclic structure in the main chain is preferably a fluorinated alicyclic structure.
  • fluorinated alicyclic structure is an “alicyclic structure” having fluorine atom(s). Further, “having a fluorinated alicyclic structure in its main chain” means that at least one of carbon atoms constituting the fluorinated alicyclic structure is a carbon atom constituting the main chain of the polymer (A).
  • fluorine atoms may be bonded to the main chain not forming a cyclic structure.
  • the fluorinated alicyclic structure may, for example, be a saturated or unsaturated hydrocarbon ring structure which may have a substituent, or one wherein some or all of hydrogen atoms in e.g. a heterocyclic structure having some of carbon atoms in such a hydrocarbon ring structure substituted by a heteroatom such as an oxygen atom, a nitrogen atom or the like, are substituted by fluorine atoms.
  • a fluorinated alicyclic structure of a heterocyclic structure having one or two etheric oxygen atoms in its cyclic skeleton is preferred. Further it is preferred that all of hydrogen atoms are substituted by fluorine atoms.
  • the polymer (A) is preferably the following fluorinated cyclic polymer (I′) or fluorinated cyclic polymer (II′).
  • Fluorinated cyclic polymer (I′) a polymer having a unit based on a cyclic fluorinated monomer.
  • Fluorinated cyclic polymer (II′) a polymer having a unit formed by cyclopolymerization of a diene-type fluorinated monomer.
  • cyclic polymer means a polymer having a cyclic structure.
  • the fluorinated cyclic polymer (I′) has a unit based on the “cyclic fluorinated monomer”.
  • cyclic fluorinated monomer is a monomer having a polymerizable double bond between carbon atoms constituting a fluorinated alicyclic ring, or a monomer having a polymerizable double bond between a carbon atom constituting a fluorinated alicyclic ring and a carbon atom of other than a fluorinated alicyclic ring.
  • Such a cyclic fluorinated monomer is preferably the following compound (1) or compound (2).
  • each of X 11 , X 12 , X 13 , X 14 , Y 11 and Y 12 which are independent of one another, is a fluorine atom, a perfluoroalkyl group or a perfluoroalkoxy group.
  • the perfluoroalkyl group for X 11 , X 12 , X 13 , X 14 , Y 11 and Y 12 has preferably from 1 to 7, more preferably from 1 to 4, carbon atoms.
  • Such a perfluoroalkyl group is preferably linear or branched, more preferably linear. Specifically, it may, for example, be a trifluoromethyl group, a pentafluoroethyl group or a heptafluoropropyl group, and particularly preferred is a trifluoromethyl group.
  • the perfluoroalkoxy group for X 11 , X 12 , X 13 , X 14 , Y 11 and Y 12 may, for example, be one having an oxygen atom (—O—) bonded to the above perfluoroalkyl group. It may specifically be a trifluoromethoxy group.
  • X 11 is preferably a fluorine atom.
  • X 12 is preferably a fluorine atom, a trifluoromethyl group or a C 1-4 perfluoroalkoxy group, more preferably a fluorine atom or a trifluoromethoxy group.
  • Each of X 13 and X 14 which are independent of each other, is preferably a fluorine atom or a C 1-4 perfluoroalkyl group, more preferably a fluorine atom or a trifluoromethyl group.
  • Each of Y 11 and Y 12 which are independent of each other, is preferably a fluorine atom, a C 1-4 perfluoroalkyl group or a C 1-4 perfluoroalkoxy group, more preferably a fluorine atom or a trifluoromethyl group.
  • X 13 and X 14 may be bonded to each other to form a second fluorinated alicyclic ring together with the carbon atoms to which X 13 and X 14 are bonded.
  • Such a second fluorinated alicyclic ring is preferably a 4- to 6-membered ring.
  • Such a second fluorinated alicyclic ring is preferably a saturated alicyclic ring.
  • Such a second fluorinated alicyclic ring may have an etheric oxygen atom (—O—) in the cyclic skeleton.
  • the number of etheric oxygen atoms in the fluorinated alicyclic ring is preferably 1 or 2.
  • Y 11 and Y 12 may be bonded to each other to form a second fluorinated alicyclic ring together with the carbon atoms to which Y 11 and Y 12 are bonded.
  • Such a second fluorinated alicyclic ring is preferably a 4- to 6-membered ring.
  • Such a second fluorinated alicyclic ring is preferably a saturated alicyclic ring.
  • Such a second fluorinated alicyclic ring may have an etheric oxygen atom (—O—) in the cyclic skeleton.
  • the number of etheric oxygen atoms in the fluorinated alicyclic ring is preferably 1 or 2.
  • Preferred specific examples of the compound (1) include compounds (1-1) to (1-5).
  • Preferred specific examples of the compound (2) include compounds (2-1) and (2-2).
  • the fluorinated cyclic polymer (I′) may be constituted solely by a unit formed by the above cyclic fluorinated monomer, or may be a copolymer having such a unit and another unit.
  • the proportion of the unit based on the cyclic fluorinated monomer is preferably at least 20 mol %, more preferably at least 40 mol %, or may be 100 mol %, based on the total of all repeating units constituting the fluorinated cyclic polymer (I′).
  • Said another monomer may be one copolymerizable with the above cyclic fluorinated monomer and is not particularly limited.
  • the after-mentioned diene-type fluorinated monomer a monomer having a reactive functional group in the side chain, tetrafluoroethylene, chlorotrifluoroethylene or perfluoro(methyl vinyl ether) may, for example, be mentioned.
  • a polymer obtainable by copolymerization of the cyclic fluorinated monomer with the diene-type fluorinated monomer is regarded as the fluorinated cyclic polymer (I′).
  • the monomer having the above reactive functional group in the side chain, copolymerizable with the above cyclic fluorinated monomer may be a fluorinated monomer such as methyl 2,2,3,3,4,4-hexafluoro-4-(1,2,2-trifluorovinyloxy)butanoate, methyl 2,2,3,3-tetrafluoro-3-(1,1,2,2,3,3-hexafluoro-3-(1,2,2-trifluorovinyloxy)propoxy)propanoate, 1,1,2,2-tetrafluoro-2-(1,1,1,2,3,3-hexafluoro-3-(1,2,2-trifluorovinyloxy)propan-2-yloxy)ethanesulfonyl fluoride or 1,1,2,2-tetrafluoro-2-(1,2,2-trifluorovinyloxy)ethanesulfonyl fluoride, or a hydrocarbon monomer such as hydroxyethyl vinyl ether, hydroxypropy
  • fluorinated cyclic polymer (I′) it is preferred to use a homopolymer of a cyclic fluorinated monomer selected from compounds (1-1), (1-3) and (2-2), or a copolymer of one cyclic fluorinated monomer selected from the three compounds with one member selected from tetrafluoroethylene, chlorotrifluoroethylene and the after-mentioned diene-type fluorinated monomer.
  • perfluorobutenyl vinyl ether CF 2 ⁇ CFOCF 2 CF 2 CF ⁇ CF 2
  • perfluoro(4-methylbutenyl) vinyl ether CF 2 ⁇ CFOCF(CF 3 )CF 2 CF ⁇ CF 2
  • perfluorobutenyl vinyl ether it is preferred to employ perfluorobutenyl vinyl ether.
  • the fluorinated cyclic polymer (II′) has a unit formed by cyclopolymerization of “a diene type fluorinated monomer”.
  • the “diene-type fluorinated monomer” is a monomer having two polymerizable double bonds and fluorine atoms. Such polymerizable double bonds are not particularly limited, but are preferably vinyl groups, allyl groups, acryloyl groups or methacryloyl groups.
  • the diene-type fluorinated monomer is preferably the following compound (3). CF 2 ⁇ CF-Q-CF ⁇ CF 2 (3)
  • Q is a C 1-5 , preferably C 1-3 , perfluoroalkylene group which may have a branch and which may have an etheric oxygen atom and wherein some of fluorine atoms may be substituted by halogen atoms other than fluorine atoms.
  • halogen atoms other than fluorine atoms may, for example, be chlorine atoms or bromine atoms.
  • Q is preferably a perfluoroalkylene group having an etheric oxygen atom, and in such a case, the etheric oxygen atom in the perfluoroalkylene group may be present at one terminal of the group or may be present at both terminals of the group, or may be present between carbon atoms of the group. From the viewpoint of the cyclopolymerizability, it is preferably present at one terminal of the group.
  • the following units (3-1) to (3-4) may be mentioned.
  • the unit to be formed by cyclopolymerization of the compound (3) more specifically, the following units (3-a) to (3-k) may be mentioned.
  • the units (3-a) to (3-k) one of x and y is 0, and the other is 1.
  • the fluorinated cyclic polymer (II′) may be constituted solely by a unit formed by cyclopolymerization of the above diene-type fluorinated monomer, or may be a copolymer having such a unit and another unit.
  • the proportion of the unit formed by cyclopolymerization of the diene-type fluorinated monomer is preferably at least 50 mol %, more preferably at least 80 mol %, most preferably 100 mol %, based on the total of all repeating units constituting the fluorinated cyclic polymer (II′).
  • Said another monomer may be one copolymerizable with the above diene-type fluorinated monomer and is not particularly limited.
  • a cyclic fluorinated monomer such as the above-mentioned compound (1) or (2), a monomer having the above reactive functional group in the side chain, tetrafluoroethylene, chlorotrifluoroethylene, or perfluoro(methyl vinyl ether) may, for example, be mentioned.
  • the monomer having the above reactive functional group in the side chain, copolymerizable with the above diene type fluorinated monomer may, for example, be a fluorinated monomer such as methyl 2,2,3,3,4,4-hexafluoro-4-(1,2,2-trifluorovinyloxy)butanoate, methyl 2,2,3,3-tetrafluoro-3-(1,1,2,2,3,3-hexafluoro-3-(1,2,2-trifluorovinyloxy)propoxy)propanoate, 1,1,2,2-tetrafluoro-2-(1,1,1,2,3,3-hexafluoro-3-(1,2,2-trifluorovinyloxy)propan-2-yloxy)ethanesulfonyl fluoride or 1,1,2,2-tetrafluoro-2-(1,2,2-trifluorovinyloxy)ethanesulfonyl fluoride, or a hydrocarbon monomer such as hydroxyethyl vinyl ether
  • fluorinated cyclic polymer (II′) it is preferred to use a homopolymer obtainable from one diene-type fluorinated monomer selected from perfluorobutenyl vinyl ether (CF 2 ⁇ CFOCF 2 CF 2 CF ⁇ CF 2 ), perfluoro(3-methylbutenyl) vinyl ether (CF 2 ⁇ CFOCF 2 CF(CF 3 )CF ⁇ CF 2 ), perfluoro(4-methylbutenyl) vinyl ether (CF 2 ⁇ CFOCF(CF 3 )CF 2 CF ⁇ CF 2 ), perfluoro(4-chlorobutenyl) vinyl ether (CF 2 ⁇ CFOCFClCF 2 CF ⁇ CF 2 ), perfluoro(4,4′-dichlorobutenyl) vinyl ether (CF 2 ⁇ CFOCCl 2 CF 2 CF ⁇ CF 2 ) and perfluoro(3-methoxybutenyl) vinyl ether (CF 2 ⁇ CFOCF 2
  • Polymer (A) has a carboxy group or an alkoxycarbonyl group as its terminal group.
  • the alkoxycarbonyl group may, for example, be a methoxycarbonyl group, an ethoxycarbonyl group, a propoxycarbonyl group, an isopropoxycarbonyl group, a butoxycarbonyl group or a tert-butoxycarbonyl group.
  • the terminal group of the polymer (A) is preferably a carboxy group, a methoxycarbonyl group or an ethoxycarbonyl group.
  • the carboxy group or the alkoxycarbonyl group may be present at a main chain terminal or at a side chain terminal, or at both the main chain terminal and the side chain terminal. From the production efficiency, it is particularly preferably present at a main chain terminal.
  • the polymer (A) having a carboxy group or an alkoxycarbonyl group at a main chain terminal may be obtained by carrying out polymerization by means of a polymerization initiator and decomposing an unstable terminal group thereby formed, by e.g. thermal treatment, to form a carbonylfluoride group (—CF ⁇ O group) at the terminal, followed by post treatment.
  • the carbonylfluoride group may be hydrolyzed to convert it to a carboxy group. Otherwise, it may be reacted with an alcohol to convert it to an alkoxycarbonyl group.
  • polymerization initiator one commonly employed may be used, and a polymerization initiator having a peroxide group is particularly preferred.
  • a polymerization initiator having a peroxide group either a hydrocarbon type polymerization initiator or a fluorinated polymerization initiator may be used.
  • hydrocarbon type polymerization initiator specifically, diisopropyl peroxydicarbonate, diisobutyl peroxydicarbonate, dipropanoic acid peroxide, dibutanoic acid peroxide, benzoic peroxide or di-tert-butyl peroxide may, for example, be used.
  • di-perfluoropropanoic acid peroxide diperfluorobutanoic acid peroxide, perfluorobenzoic peroxide or di-perfluoro tert-butyl peroxide may, for example, be used.
  • the polymer (A) is preferably amorphous, since it is thereby excellent in the solubility in a solvent and has good compatibility with the after-described silane coupling agent.
  • the weight average molecular weight of polymer (A) is preferably at least 50,000, more preferably at least 150,000, further preferably at least 200,000, particularly preferably at least 250,000. If the weight average molecular weight is less than 50,000, film formation tends to be difficult. When it is at least 200,000, the heat resistance of the film will be improved, and the thermal stability as an electret will be improved.
  • the weight average molecular weight of the polymer (A) is preferably at most 1,000,000, more preferably at most 850,000, further preferably at most 650,000, particularly preferably at most 550,000.
  • the intrinsic viscosity of the polymer (A) correlates with the molecular weight of the polymer (A). Accordingly, it preferably has an intrinsic viscosity corresponding to the above preferred molecular weight.
  • a specific preferred intrinsic viscosity value varies depending upon the units constituting the polymer (A).
  • the intrinsic viscosity (30° C.) is preferably from 0.1 to 0.9 dl/g, more preferably from 0.2 to 0.8 dl/g, most preferably from 0.3 to 0.6 dl/g.
  • Such an intrinsic viscosity is a value measured by using e.g. perfluoro(2-butyltetrahydrofuran) as a solvent.
  • the polymer (A) preferably has a relative dielectric constant of from 1.8 to 8.0, more preferably from 1.8 to 5.0, particularly preferably from 1.8 to 3.0, in consideration of the charge retention performance.
  • a relative dielectric constant is a value measured at a frequency of 1 MHz in accordance with ASTM D150.
  • the polymer (A) one having a high volume resistivity and a high dielectric breakdown voltage is preferred.
  • the volume resistivity of the polymer (A) is preferably from 10 10 to 10 20 ⁇ cm, more preferably from 10 16 to 10 19 ⁇ cm. Such a volume resistivity is measured in accordance with ASTM D257.
  • the dielectric breakdown voltage of the polymer (A) is preferably from 10 to 25 kV/mm, more preferably from 15 to 22 kV/mm. Such a dielectric breakdown voltage is measured in accordance with ASTM D149.
  • the polymer (A) one having high hydrophobicity is preferred in order to exclude water which may be adversely influential over the insulating property and to maintain a high insulating property.
  • a commercial product may be used as the polymer (A).
  • a commercial product of a fluorinated polymer which has an alicyclic structure containing an etheric oxygen atom in its main chain and which has a carboxy group or an alkoxycarbonyl group at a main chain terminal CYTOP (registered trademark, manufactured by Asahi Glass Company, Limited) may be mentioned.
  • the silane coupling agent to be used in the present invention is a silane coupling agent having an amino group.
  • a silane coupling agent having an amino group the following ones may be exemplified.
  • the silane coupling agent having an amino group may simply be referred to as the silane coupling agent.
  • a dialkoxysilane such as ⁇ -aminopropylmethyldiethoxysilane, ⁇ -aminopropylmethyldimethoxysilane, N-( ⁇ -aminoethyl)- ⁇ -aminopropylmethyldimethoxysilane or N-( ⁇ -aminoethyl)- ⁇ -aminopropylmethyldiethoxysilane.
  • a trialkoxysilane such as ⁇ -aminopropyltrimethoxysilane, ⁇ -aminopropyltriethoxysilane, N-( ⁇ -aminoethyl)- ⁇ -aminopropyltrimethoxysilane or N-( ⁇ -aminoethyl)- ⁇ -aminopropyltriethoxysilane.
  • a silane coupling agent having an aromatic amine structure such as a compound represented by the following formula (s1) or (s2): ArSi(OR 21 )(OR 22 )(OR 23 ) (s1) ArSiR 24 (OR 21 )(OR 22 ) (s2) [wherein each of R 21 to R 24 which are independent of one another is a hydrogen atom, a C 1-20 alkyl group or an aryl group, and Ar is a p-, m- or o-aminophenyl group.]
  • silane coupling agents may be used alone, or two or more of them may be used in combination.
  • a partially hydrolyzed condensate of the above silane coupling agent it is also preferred to use a co-partially hydrolyzed condensate of the above silane coupling agent with a tetraalkoxysilane such as tetramethoxysilane, tetraethoxysilane or tetrapropoxysilane.
  • a particularly preferred silane coupling agent is at least one member selected from ⁇ -aminopropylmethyldiethoxysilane, ⁇ -aminopropylmethyldimethoxysilane, N-( ⁇ -aminoethyl)- ⁇ -aminopropylmethyldimethoxysilane, N- ⁇ -aminoethyl)- ⁇ -aminopropylmethyldiethoxysilane, ⁇ -aminopropyltrimethoxysilane, ⁇ -aminopropyltriethoxysilane, N-( ⁇ -aminoethyl)- ⁇ -aminopropyltrimethoxysilane, N-( ⁇ -aminoethyl)- ⁇ -aminopropyltriethoxysilane and aminophenyltrimethoxysilane.
  • the content of the silane coupling agent is preferably from 0.1 to 20 mass %, more preferably from 0.3 to 10 mass %, most preferably from 0.5 to 5 mass %, based on the total amount of the polymer (A) and the silane coupling agent. Within such a range, it can be uniformly mixed with the polymer (A), and it is unlikely to undergo phase separation in the solution.
  • the combination of the fluorinated polymer and the silane coupling agent preferred is a combination of, as the fluorinated polymer, one member selected from a copolymer of the above compound (1-1) with tetrafluoroethylene or a diene-type fluorinated monomer, and a homopolymer of the after-mentioned diene-type fluorinated monomer, and, as the silane coupling agent, one member selected from ⁇ -aminopropylmethyldiethoxysilane, ⁇ -aminopropylmethyldimethoxysilane, N-( ⁇ -aminoethyl)- ⁇ -aminopropylmethyldimethoxysilane, N-( ⁇ -aminoethyl)- ⁇ -aminopropylmethyldiethoxysilane, ⁇ -aminopropyltrimethoxysilane, ⁇ -aminopropyltriethoxysilane, N-( ⁇ -amino
  • diene-type fluorinated monomer it is preferred to employ perfluorobutenyl vinyl ether (CF 2 ⁇ CFOCF 2 CF 2 CF ⁇ CF 2 ) or perfluoro(4-methylbutenyl) vinyl ether (CF 2 ⁇ CFOCF(CF 3 )CF 2 CF ⁇ CF 2 ), and it is most preferred to employ perfluorobutenyl vinyl ether.
  • perfluorobutenyl vinyl ether CF 2 ⁇ CFOCF 2 CF 2 CF ⁇ CF 2
  • perfluoro(4-methylbutenyl) vinyl ether CF 2 ⁇ CFOCF(CF 3 )CF 2 CF ⁇ CF 2
  • a composition comprising the polymer (A) and the silane coupling agent is made into a coating fluid by means of a solvent.
  • a solvent to dissolve the polymer (A) and a solvent to dissolve the silane coupling agent in combination.
  • a fluorinated organic solvent may, for example, be used.
  • an aprotic fluorinated solvent is preferred.
  • the aprotic fluorinated solvent is a fluorinated solvent having no proton-donating property.
  • aprotic fluorinated solvents the following fluorinated compounds may be exemplified.
  • a polyfluoro aromatic compound such as perfluorobenzene, pentafluorobenzene, 1,3-bis(trifluoromethyl)benzene or 1,4-bis(trifluoromethyl)benzene; a polyfluorotrialkylamine compound such as perfluorotributylamine or perfluorotripropylamine; a polyfluorocycloalkane compound such as perfluorodecalin, perfluorocyclohexane or perfluoro(1,3,5-trimethylcyclohexane); a polyfluoro cyclic ether compound such as perfluoro(2-butyltetrahydrofuran); a perfluoropolyether; and a polyfluoroalkane compound such as perfluorohexane, perfluorooctane, perfluorodecane, perfluorododecane, perfluoro(2,7-dimethyloctane), 1,1,2-trichlor
  • aprotic fluorinated solvents may be used alone or in combination as a mixture.
  • HFE hydrofluoroether
  • R a —O—R b wherein R a is a C 5-12 linear or branched polyfluoroalkyl group which may have an ether bond, and R b is a C 1-5 linear or branched alkyl group or polyfluoroalkyl group
  • the number of carbon atoms in R a is 4 or less, it is difficult to dissolve the polymer (A), and if the number of carbon atoms in R a exceeds 13, it is difficult to obtain such a solvent industrially. Therefore, the number of carbon atoms in R a is selected within a range of from 5 to 12. The number of carbon atoms in R a is preferably from 6 to 10, more preferably from 6 to 7, or from 9 to 10.
  • a polyfluoroalkyl group is a group having at least two of hydrogen atoms in an alkyl group substituted by fluorine atoms and includes a perfluoroalkyl group having all of hydrogen atoms in an alkyl group substituted by fluorine atoms, or a group having at least two of hydrogen atoms in an alkyl group substituted by fluorine atoms, and having at least one of hydrogen atoms in the alkyl group substituted by a halogen atom other than a fluorine atom.
  • a halogen atom other than a fluorine atom a chlorine atom is preferred.
  • the polyfluoroalkyl group is preferably a group having at least 60%, more preferably at least 80%, in number of hydrogen atoms of the corresponding alkyl group substituted by fluorine atoms.
  • a more preferred polyfluoroalkyl group is a perfluoroalkyl group.
  • the number of ether bonds in R a is preferably from 1 to 3, more preferably from 1 to 2.
  • R b is a methyl group, an ethyl group, a trifluoroethyl group, a tetrafluoroethyl group, a tetrafluoropropyl group or the like.
  • the molecular weight of HFE is too high, not only the viscosity of the coating fluid will be increased, but also the solubility of the polymer (A) will be lowered, and accordingly, it is preferably at most 1,000.
  • the fluorine content in HFE is preferably from 60 to 80 wt %.
  • the following ones may be exemplified.
  • (CF 3 ) 2 CFCF(OCH 3 )CF 2 CF 3 is particularly suitable as the solvent.
  • HFE may be used alone or in combination as a mixture.
  • the fluorinated organic solvent to dissolve the polymer (A) it is preferred to use only an aprotic fluorinated solvent, since it has a large dissolving power and is a good solvent.
  • the boiling point of the fluorinated organic solvent to dissolve the polymer (A) is preferably from 65 to 220° C.
  • the boiling point of the fluorinated organic solvent is at least 100° C., a uniform film can easily be formed at the time of the coating.
  • a protic fluorinated solvent is a fluorinated solvent having a proton-donating property.
  • protic fluorinated solvents the following ones may be exemplified.
  • a fluorinated alcohol such as trifluoroethanol, 2,2,3,3,3-pentafluoro-1-propanol, 2-(perfluorobutyl)ethanol, 2-(perfluorohexyl)ethanol, 2-(perfluorooctyl)ethanol, 2-(perfluorodecyl)ethanol, 2-(perfluoro-3-methylbutyl)ethanol, 2,2,3,3-tetrafluoro-1-propanol, 2,2,3,3,4,4,5,5-octafluoro-1-pentanol, 2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoro-1-heptanol, 2,2,3,3,4,4,5,5,6,6,7,7,8,8-hexadecafluoro-1-nonanol, 1,1,1,3,3,3-hexafluoro-2-propanol or 1,3,3,4,4,4-hexafluoro-2-butanol.
  • a fluorinated carboxylic acid such as trifluoroacetic acid, perfluoropropanoic acid, perfluorobutanoic acid, perfluoropentanoic acid, perfluorohexanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid, perfluorononanoic acid, perfluorodecanoic acid, 1,1,2,2-tetrafluoropropanoic acid, 1,1,2,2,3,3,4,4-octafluoropentanoic acid, 1,1,2,2,3,3,4,4,5,5-dodecafluoroheptanoic acid or 1,1,2,2,3,3,4,4,5,5,6,6-hexadecafluorononanoic acid, an amide of such a fluorinated carboxylic acid, a fluorinated sulfonic acid such as trifluoromethanesulfonic acid or heptadecafluorooctanesulfonic acid,
  • protic fluorinated solvents may be used alone or in combination as a mixture of two or more of them.
  • the water content in the solvent to be used for the preparation of the coating fluid should better be small, and it is preferably at most 100 mass ppm, more preferably at most 20 mass ppm.
  • the concentration of the polymer (A) in the coating fluid is preferably from 0.1 to 30 mass %, more preferably from 0.5 to 20 mass %.
  • the solid content concentration in the coating fluid may be suitably set depending upon the thickness of the film to be formed. It is usually from 0.1 to 30 mass %, preferably from 0.5 to 20 mass %.
  • the coating fluid having the mass measured is heated under ordinary pressure at 200° C. for one hour to distill the solvent off, and the mass of the remaining solid content is measured, whereupon the solid content is calculated.
  • the coating fluid may contain a tetraalkoxysilane such as tetramethoxysilane, tetraethoxysilane or tetrapropoxysilane in addition to the polymer (A), the silane coupling agent having an amino group and the above solvent.
  • a tetraalkoxysilane such as tetramethoxysilane, tetraethoxysilane or tetrapropoxysilane in addition to the polymer (A), the silane coupling agent having an amino group and the above solvent.
  • the coating fluid is preferably obtained by preparing a polymer (A) solution having the polymer (A) dissolved in an aprotic fluorinated solvent and a silane coupling agent solution having the silane coupling agent dissolved in a protic fluorinated solvent, respectively, and then mixing the polymer (A) solution and the silane coupling agent solution.
  • a substrate is coated with the coating fluid obtained in the coating fluid-preparation step, to form a coating layer comprising the polymer (A) and the silane coupling agent.
  • the coating method may, for example, be a roll coater method, a casting method, a dipping method, a spin coating method, a casting-on-water method, a Langmuir•Blodgett method, a die coating method, an ink jet method or a spray coating method. Otherwise, a printing technique such as a relief printing method, a gravure printing method, a planographic printing method, a screen printing method or a flexo printing method, may also be used.
  • any substrate may be used without selecting the material, so long as it is a substrate which can be earthed at the time of injecting an electric charge to the coating layer obtained by the coating.
  • a preferred material may, for example, be an electrically conductive metal such as gold, platinum, copper, aluminum, chromium or nickel.
  • an insulating material such as an inorganic material such as glass, or an organic polymer material such as polyethylene terephthalate, polyimide, polycarbonate or an acrylic resin, so long as it is one having its surface coated with an electroconductive metal film by a method such as sputtering, vapor deposition or wet coating.
  • a semiconductor material such as silicon may also be used so long as it is one having similar surface treatment applied or one where the resistance value of the semiconductor material itself is low.
  • the resistance value of the substrate material is preferably at most 0.1 ⁇ cm, particularly preferably at most 0.01 ⁇ cm, by volume resistivity.
  • the substrate may be a flat plate having a smooth surface or may be one having convexoconcave formed. Otherwise, it may have patterning applied in various shapes.
  • convexoconcave or a pattern may be formed on the insulating material itself, or convexoconcave or a pattern may be formed on a metal layer applied on the surface.
  • the method for forming convexoconcave or a pattern on the substrate is not particularly limited, and a conventional method may be used.
  • a vacuum process or a wet system process may be employed as the method for forming convexoconcave or a pattern.
  • Specific examples of such a method include, as the vacuum process, a sputtering method via a mask and a vapor deposition method via a mask; and, as the wet system process, a roll coater method, a casting method, a dipping method, a spin coating method, a casting-on-water method, a Langmuir Blodgett method, a die coating method, an ink jet method, a spray coating method, etc.
  • a printing technique such as a relief printing method, a gravure printing method, a planographic printing method, a screen printing method or a flexo printing method may also be used.
  • a method for forming fine convexoconcave or pattern a nanoimprinting method or a photolithography method may also be used.
  • the shape and size of the coating layer may suitably be set depending on the shape and size of the desired electret.
  • the electret is usually used in the form of a film having a thickness of from 1 to 200 ⁇ m. It is particularly preferred to employ it in the form of a film having a thickness of from 10 to 20 ⁇ m, from the viewpoint of the characteristics as an electret and processing efficiency.
  • the thickness of the coating layer may be made to be from 2 to 220 ⁇ m, preferably from 12 to 25 ⁇ m.
  • the substrate may be peeled after the electric charge-injection step.
  • the above coating layer is thermally treated at a specific temperature to obtain a coating film (the coating film obtained by the thermal treatment of the coating layer may hereinafter sometimes be referred to as a coating film).
  • the thermal treatment preferably comprises a preliminary drying step and the main drying/baking step.
  • the solvent in the coating layer is evaporated as far as possible to preliminarily dry the coating layer.
  • the preliminary drying step it is possible to prevent foaming of the film, surface roughening, non-uniformity, etc. in the subsequent main drying/baking step.
  • the preliminary drying step is preferably carried out at a temperature of not higher than the boiling point of the solvent. Specifically, the temperature is preferably from 50 to 150° C., more preferably from 80 to 120° C.
  • the time for the preliminary drying step is preferably from 0.1 to 5 hours, more preferably from 0.5 to 2 hours.
  • the main drying/baking step is carried out within a range of from 250° C. to 330° C.
  • the temperature (baking temperature) in the main drying/baking step is preferably within a range of from 260° C. to 300° C., more preferably from 260 to 280° C.
  • the time for the baking step is preferably from 0.5 to 5 hours, more preferably from 1 to 2 hours.
  • the atmosphere for the main drying/baking step may be an inert gas atmosphere or an air atmosphere, but an air atmosphere is preferred for the formation of amide bonds which will be described hereinafter. Further, the pressure is preferably ordinary pressure.
  • another layer may be laminated on the coating film obtained by thermal treatment of the coating layer comprising the above polymer (A) and the silane coupling agent.
  • a protective layer a layer composed solely of the polymer (A) or a layer composed of an inorganic substance, may, for example, be mentioned.
  • Such another layer may be formed on the coating film after the thermal treatment step, or another layer may be formed at a stage where the preliminary drying step in the thermal treatment step has been completed and may be baked together with the coating layer comprising the polymer (A) and the silane coupling agent.
  • any method may be employed without selecting the means, so long as it is a common method for charging an insulating material.
  • a corona discharge method disclosed in e.g. G. M. Sessler, Electrets Third Edition, pp 20, Chapter 2.2 “Charging and Polarizing Methods” (Laplacian Press, 1998), or an electron beam bombardment method, an ion beam bombardment method, a radiation method, a light irradiation method, a contact charging method or a liquid contact charging method.
  • a corona discharge method or an electron beam bombardment method it is preferred to employ a corona discharge method or an electron beam bombardment method.
  • the temperature condition at the time of injecting an electric charge it is preferred to carry out the injection at a temperature of at least the glass transition temperature of the polymer (A) from the viewpoint of the stability of the electric charge to be maintained after the injection, and it is particularly preferred to carry out the injection under a temperature condition at a level of the glass transition temperature+10 to 20° C.
  • the voltage to be applied at the time of injecting an electric charge it is preferred to apply a high voltage so long as it is lower than the insulation breakdown voltage of the coating film of the polymer (A) and its composition.
  • the coating film in the present invention it is possible to apply a high voltage of from ⁇ 6 to ⁇ 30 kV, and it is particularly preferred to apply a voltage of from ⁇ 8 to ⁇ 15 kV.
  • the polymer (A) to be used for the coating film is a fluorinated polymer, whereby a negative charge can be maintained more stably than a positive charge, and it is further preferred to apply a voltage of from ⁇ 8 to ⁇ 15 kV.
  • the electret of the present invention is useful for an electrostatic induction conversion device to covert electric energy to kinetic energy.
  • Such an electrostatic induction conversion device may, for example, be a vibration-type power-generating unit, a microphone, a speaker, an actuator or a sensor.
  • the structure of such an electrostatic induction conversion device may be the same as a conventional one except that as the electret, the electret of the present invention is used.
  • the electret obtained by the present invention has high stability with time and thermal stability of retained electric charge and has excellent charge retention performance.
  • the electrostatic induction conversion device of the present invention comprising such an electret has such features that deterioration of properties is less likely to occur, and dependence of the properties on the environment is small.
  • composition comprising the polymer (A) and the silane coupling agent having an amino group, it is possible not only to improve the adhesion to a substrate of the coating film made of such a composition but also to improve the thermal stability of an electric charge maintained by the electret prepared therefrom.
  • the reason as to why the thermal stability is improved by incorporating the polymer (A) and the silane coupling agent having an amino group, is considered to be such that the polymer (A) and the silane coupling agent induce a nano phase separation to form a nano cluster structure derived from the silane coupling agent, and such a nano cluster structure will function as a site to store an electric charge in the electret.
  • the composition comprising the polymer (A) and the silane coupling agent having an amino group will have the thermal stability improved by the thermal treatment. It is considered that by the thermal treatment, the following reactions are promoted, whereby the thermal motion of a nano cluster structure derived from the silane coupling agent will be suppressed, and the nano cluster structure will be stabilized.
  • the thermal stability was high when the temperature for the heat treatment was within a range of from 250 to 330° C., and it was particularly high within a range of from 260 to 300° C.
  • the content of the amide group to be formed by the reaction (1) has been found to be high when the temperature for the heat treatment is within a range of from 250 to 330° C., and is higher within a range of from 260 to 300° C. This indicates that if the temperature becomes too high, the formed amide group is likely to be thermally decomposed.
  • the dielectric breakdown voltage is a value measured in accordance with ASTM D149.
  • the relative dielectric constant is a value measured in accordance with ASTM D150 at a frequency of 1 MHz.
  • the intrinsic viscosity [ ⁇ ] (30° C.) (unit: dl/g) is a value measured by an Ubbelohde viscometer at 30° C. by using perfluoro(2-butyltetrahydrofuran) as a solvent.
  • the weight average molecular weight is a value calculated from the above intrinsic viscosity in accordance with the following relational formula disclosed in Journal of Chemical Society of Japan, 2001, NO. 12, P. 661.
  • the measurement of the film thickness was carried out by using optical interfero type film thickness measuring apparatus C10178 manufactured by Hamamatsu Photonics K.K.
  • Polymer A1 was thermally treated in air at 250° C. for 8 hours and then immersed in water to obtain polymer A2 having a —COOH group as its terminal group.
  • the IR spectrum of a compression-molded film of such a polymer was measured, whereby a characteristic absorption was observed at 1,775 and 1,810 cm ⁇ 1 attributable to the —COOH group.
  • the intrinsic viscosity [ ⁇ ] (30° C.) of this polymer was 0.24 dl/g, and the weight average molecular weight of the polymer quantified from such a result was 177,000. From these results, the product prepared by the above method was confirmed to be a fluorinated polymer having an alicyclic structure in its main chain and at the same time, having a carboxy group or an alkoxycarbonyl group as its terminal group.
  • the volume resistivity of polymer A2 was >10 17 ⁇ cm, the dielectric breakdown voltage was 19 kV/mm, and the relative dielectric constant was 2.1.
  • polymer solution P1 In perfluorotributylamine, the above polymer A2 was dissolved at a concentration of 15 mass % to obtain polymer solution P1.
  • a solution having 10.6 g of perfluorotributylamine added to 84.6 g of the above polymer solution P1 was prepared.
  • a silane coupling agent solution (a solution having 0.4 g of ⁇ -aminopropylmethyldiethoxysilane dissolved in 4.7 g of 2-(perfluorohexyl)ethanol) was mixed to obtain a uniform polymer composition solution M1.
  • Polymer B1 was thermally treated in air at 250° C. for 8 hours and then immersed in water to obtain polymer B2 having a —COOH group as its terminal group.
  • the IR spectrum of a compression-molded film of such a polymer was measured, whereby a characteristic absorption was observed at 1,775 and 1,810 cm ⁇ 1 attributable to the —COOH group.
  • the intrinsic viscosity [ ⁇ ] (30° C.) of this polymer was 0.32 dl/g, and the weight average molecular weight of the polymer quantified from such a result was 287,000. From these results, the product prepared by the above method was confirmed to be a fluorinated polymer having an alicyclic structure in its main chain and at the same time, having a carboxy group or an alkoxycarbonyl group as its terminal group.
  • the volume resistivity of polymer B2 was >10 17 ⁇ cm, the dielectric breakdown voltage was 19 kV/mm, and the relative dielectric constant was 2.1.
  • silane coupling agent solution (a solution having 0.3 g of ⁇ -aminopropylmethyldiethoxysilane dissolved in 4.4 g of 2-(perfluorohexyl)ethanol) was mixed to obtain a uniform polymer composition solution M2.
  • Polymer B1 was thermally treated in air at 250° C. for 8 hours and then immersed in water to obtain polymer C2 having a —COOH group as its terminal group.
  • the infrared absorption spectrum of a compression-molded film of such a polymer was measured, whereby a characteristic absorption was observed at 1,775 and 1,810 cm ⁇ 1 attributable to the —COOH group.
  • the intrinsic viscosity [ ⁇ ] (30° C.) of this polymer was 0.45 dl/g, and the weight average molecular weight of the polymer quantified from such a result was 506,000. From these results, the product prepared by the above method was confirmed to be a fluorinated polymer having an alicyclic structure in its main chain and at the same time, having a carboxy group or an alkoxycarbonyl group as its terminal group.
  • the volume resistivity of polymer C2 was >10 17 ⁇ cm, the dielectric breakdown voltage was 19 kV/mm, and the relative dielectric constant was 2.1.
  • a silane coupling agent solution (a solution having 0.1 g of ⁇ -aminopropylmethyldiethoxysilane dissolved in 2.4 g of 2-(perfluorohexyl)ethanol) was mixed to obtain a uniform polymer composition solution M3.
  • Polymer (A1) obtained in Preparation Example 1 was thermally treated in air at 250° C. for 8 hours and then immersed in methanol to obtain polymer A3 having a —COOCH 3 group as its terminal group.
  • the IR spectrum of a compression-molded film of the polymer was measured, whereby a characteristic absorption was observed at 1,795 cm ⁇ 1 attributable to the —COOCH 3 group.
  • the intrinsic viscosity [ ⁇ ] (30° C.) of this polymer is 0.24 dl/g, and the weight average molecular weight of the polymer quantified from this result was 177,000. From these results, the product prepared by the above method was confirmed to be a fluorinated polymer having an alicyclic structure in its main chain and at the same time, having a carbonyl group or an alkoxycarbonyl group as its terminal group.
  • the volume resistivity of polymer A3 was >10 17 ⁇ cm, the dielectric breakdown voltage was 19 kV/mm, and the relative dielectric constant was 2.1.
  • silane coupling agent solution (a solution having 0.07 g of ⁇ -aminopropylmethyldiethoxysilane dissolved in 1.2 g of 2-(perfluorohexyl)ethanol) was mixed to obtain a uniform polymer composition solution M4.
  • the IR spectrum of polymer D1 was measured, and from the absorbance of absorption at 1,930 cm ⁇ 1 , the repeating unit based on PDD (PDD content) contained in the polymer D1 was determined to be 52 mol %.
  • Such polymer D1 was thermally treated in air at 330° C. for 5 hours and then immersed in water to obtain polymer D2.
  • a compression-molded film of the polymer D2 was prepared, and the IR spectrum of such a molded film was measured, whereby the characteristic absorption was observed at 1,775 cm ⁇ 1 and 1,810 cm ⁇ 1 attributable to the —COOH group.
  • the intrinsic viscosity [ ⁇ ] (30° C.) of polymer D2 was 0.36 dl/g, the volume resistivity was >10 17 ⁇ cm, and the relative dielectric constant was 2.0.
  • a solution having 14 g of perfluorotributylamine added to 76.9 g of the above polymer solution P5 was prepared.
  • a silane coupling agent solution (a solution having 0.4 g of ⁇ -aminopropylmethyldiethoxysilane dissolved in 4.4 g of 2-(perfluorohexyl)ethanol) was mixed to obtain a uniform polymer composition solution M5.
  • silane coupling agent solution (a solution having 0.13 g of ⁇ -aminopropylmethyldiethoxysilane dissolved in 2.6 g of 2-(perfluorohexyl)ethanol) was mixed to obtain a uniform polymer composition solution M6.
  • the intrinsic viscosity (30° C.) of the polymer E1 was measured, and found to be 0.31 dl/g.
  • the polymer E1 was thermally treated in air at 250° C. for 8 hours and then immersed in water to obtain polymer E2 having a —COOH group as its terminal group.
  • the IR spectrum of a compression-molded film of the polymer was measured, whereby the characteristic absorption was observed at 1,775 cm ⁇ 1 and 1,810 cm ⁇ 1 attributable to the —COOH group.
  • the volume resistivity of the polymer E2 was >10 17 ⁇ cm, and the relative dielectric constant was 2.0. Further, the glass transition temperature measured by differential scanning calorimetry (DSC) was 124° C.
  • a solution having 4.6 g of perfluorotributylamine added to 24 g of the above polymer solution P7 was prepared.
  • a silane coupling agent solution (a solution having 0.1 g of ⁇ -aminopropylmethyldiethoxysilane dissolved in 1.3 g of 2-(perfluorohexyl)ethanol) was mixed to obtain a uniform polymer composition solution M7.
  • a silane coupling agent solution (a solution having 0.3 g of ⁇ -aminopropylmethyldiethoxysilane dissolved in 3.5 g of 2-(perfluorohexyl)ethanol) was mixed to obtain a uniform polymer composition solution M8.
  • a silane coupling agent solution (a solution having 0.4 g of N-( ⁇ -aminoethyl)- ⁇ -aminopropyltriethoxysilane dissolved in 3.5 g of 2-(perfluorohexyl)ethanol) was mixed to obtain a uniform polymer composition solution M9.
  • a silane coupling agent solution (a solution having 0.2 g of N-( ⁇ -aminoethyl)- ⁇ -aminopropylmethyldimethoxysilane dissolved in 2.5 g of 2-(perfluorohexyl)ethanol) was mixed to obtain a uniform polymer composition solution M10.
  • a silane coupling agent solution (a solution having 0.2 g of m-aminophenyltrimethoxysilane dissolved in 5.0 g of 2-(perfluorohexyl)ethanol) was mixed to obtain a uniform polymer composition solution M11.
  • a silane coupling agent solution (a solution having 0.3 g of N-( ⁇ -aminoethyl)- ⁇ -aminopropylmethyldimethoxysilane dissolved in 4.3 g of 2-(perfluorohexyl)ethanol) was mixed to obtain a uniform polymer composition solution M12.
  • a silane coupling agent solution (a solution having 0.2 g of m-aminophenyltrimethoxysilane dissolved in 6.5 g of 2-(perfluorohexyl)ethanol) was mixed to obtain a uniform polymer composition solution M13.
  • a copper substrate (3 cm square, thickness: 300 ⁇ m) was coated with the polymer composition solution M1 by a spin coating method, followed by pretreatment at 100° C. for one hour, and then, thermal treatment was carried out at a thermal treatment temperature of 300° C. for one hour to form a coating film having a thickness of 15 ⁇ m.
  • Example 1 To this coating film, injection of electric charge was carried out by means of a corona charging equipment of which a schematic diagram is shown in FIG. 1 , to obtain an electret in Example 1.
  • This corona charging equipment is designed so that by using the above copper substrate (hereinafter referred to as “the copper substrate 10 ”) having the coating film 11 (hereinafter referred to as “the coating film 11 ”) as an electrode, a high voltage can be applied between a corona needle 14 and the copper substrate 10 by a DC high voltage power source 12 (HAR-20R5, manufactured by Matsusada Precision Inc.). Further, it is designed that to a grid 16 , a grid voltage can be applied from a grid power source 18 . It is thereby designed that negative ions discharged from the corona needle 14 are homogenized by the grid 16 and then showered down on the coating film 11 , whereby electric charge is injected.
  • a DC high voltage power source 12 (HAR-20R5, manufactured by Matsusada Precision Inc.)
  • a grid voltage can be applied from a grid power source 18 . It is thereby designed that negative ions discharged from the corona needle 14 are homogenized by the grid 16 and then showered down on the
  • the coating film 11 can be heated to a temperature of at least the glass transition temperature during the electric charge-injection step.
  • 17 is an ammeter.
  • Example 1 the heating temperature of the coating film 11 by the hotplate 19 was adjusted to 120° C. which is higher by 12° C. than the glass transition temperature (Tg: 108° C. in the case of polymer A2) of the polymer (polymer A2) used.
  • Tg glass transition temperature
  • a high voltage of ⁇ 8 kV was applied for three minutes between the corona needle 14 and the copper substrate 10 in the atmospheric air atmosphere. Further, during the period, the grid voltage was set to be ⁇ 1,100 V.
  • each surface voltage in Table 1 is an average value obtained by measuring surface voltages at 9 measuring points (set in a lattice arrangement for every 3 mm from the center of the film, as shown in FIG. 2 ) of each electret by means of a surface voltmeter (model 279, manufactured by Monroe Electronics Inc.) (the same applies in Table 2 et seq.).
  • the surface voltage at the time when after exerting a thermal history of 10 minutes in an oven adjusted to 260° C., to the electret after measuring the surface voltage before heating at 260° C., the electret was returned to ordinary temperature.
  • Example or Comparative Example An electret in each Example or Comparative Example was prepared in the same manner as in Example 1 except that the polymer composition solution was the polymer composition solution in Tables 1 and 2, and the temperature for the thermal treatment was adjusted to the value in Tables 1 and 2.
  • the surface voltage (absolute value) after heating at 260° C. exceeded 200 V as the value required for ECM.
  • Example or Comparative Example An electret in each Example or Comparative Example was prepared in the same manner as in Example 1 except that the polymer composition solution was the polymer composition solution in Tables 3 to 5, the temperature for the thermal treatment and the grid voltage were adjusted to the values in Tables 3 to 5, and the temperature for heating the coating film in the charge-injection step was adjusted to the following temperature which is higher by 12° C. than the glass transition temperature of the polymer used.
  • the surface voltage at the time when after exerting a thermal history of 100 hours in an oven adjusted to 125° C., to the electret after measuring the surface voltage before heating at 125° C., the electret was returned to ordinary temperature.
  • Example or Comparative Example An electret in each Example or Comparative Example was prepared in the same manner as in Example 1 except that the polymer composition solution was the polymer composition solution in Tables 6 to 8, the temperature for the thermal treatment and the grid voltage were adjusted to the values in Tables 6 to 8, and the temperature for heating the coating film in the electric charge injection step was adjusted to the following temperature which is higher by 12° C. than the glass transition temperature of the polymer used.
  • a counter electrode 20 was disposed to face an electret 21 on a copper substrate 10 (the same as the copper substrate 10 in FIG. 1 ).
  • the discharge peak temperature represents a temperature at which the current value detected at the time of the discharge becomes maximum
  • the discharge initiation temperature represents a temperature at the time when the current value obtained by the following formula (the current value at the initiation of the discharge) was detected by the ammeter 22 .
  • Current value at the initiation of the discharge ⁇ (current value at the discharge peak temperature) ⁇ (current value before the discharge) ⁇ 0.1+(current value before the discharge)
  • the TSD test is a test by a method so-called a Thermal Stimulated Discharge method (hereinafter referred to as a TSD method).
  • a capacitor will be formed by the electret 21 and the counter electrode 20 . Accordingly, when the electret 21 is heated, the electric charge trapped in the film tends to be unstable, and if electric charge in the vicinity of the surface diminishes by e.g. diffusion, the electric charge stored in the counter electrode 20 will also decrease. Thus, by measuring the electric current value flowing from the counter electrode 20 , the thermal stability of each electret can be evaluated.
  • both of the discharge peak temperature and the discharge initiation temperature are important, but the discharge initiation temperature is particularly important. It is said that the higher these temperatures, the higher the thermal stability of the electret.
  • the polymer composition solution M1 was cast to form a film, which was subjected to pretreatment at 100° C. for one hour and then thermally treated for one hour at the heat treatment temperature disclosed in Table 7 and peeled from the PTFE sheet to obtain a cast film having a thickness of from 50 to 100 ⁇ m.
  • the infrared absorption spectrum of each cast film was measured by means of AVATAR370FT-IR manufactured by Thermo Nicolet, whereupon the areas of the absorption at 1,670 cm ⁇ 1 (hereinafter referred to as peak ( ⁇ )) derived from the amino group of ⁇ -aminopropylmethyldiethoxysilane (N—H bending vibration), the absorption at 1,730 cm ⁇ 1 (hereinafter referred to as peak ( ⁇ )) derived from the carbonyl group of an amide group formed by a reaction of ⁇ -aminopropylmethyldiethoxysilane with the terminal group COOH group of polyperfluorobutenyl vinyl ether A2, and the absorption at from 2,800 cm ⁇ 1 to 3,000 cm ⁇ 1 (hereinafter referred to as peak (y)) derived from the C—H bond of the ethoxy group of ⁇ -aminopropylmethyldiethoxysilane, were quantified.
  • peak ( ⁇ ) the absorption at
  • the peak area-standardized value of peak ( ⁇ ) derived from the amino group of ⁇ -aminopropylmethyldiethoxysilane decreased as the temperature became high, and it became a value close to substantially zero at a temperature of at least 280° C.
  • the temperature for the thermal treatment should better be high, but should be sufficient if it is at least 280° C.
  • the peak area-standardized value of peak ( ⁇ ) derived from the carbonyl group of the amide group formed by a reaction of ⁇ -aminopropylmethyldiethoxysilane with the terminal group COOH group of polyperfluorobutenyl vinyl ether A2 increases as the temperature rises, i.e. as the peak area-standardized value of peak ( ⁇ ) decreases, within a range of from 250° C. to 260° C. However, at a temperature of at least 250° C. to 260° C., it becomes substantially constant, and when the temperature exceeds 300° C., it decreases.
  • peak area-standardized value of peak ( ⁇ ) derived from the C—H bond of the ethoxy group of ⁇ -aminopropylmethyldiethoxysilane decreased as the temperature rose and became 0.7 at 330° C.
  • the temperature for the thermal treatment at which preferred results were obtained in Test Examples 1 to 3 corresponds to the temperature for the thermal treatment at which bonding of the polymer (A) and the silane coupling agent is promoted and maintained, and at which the condensation reaction of a silane coupling agent is promoted.
  • the polymer composition solution M1 was cast to form a film, which was dried under conditions of 100° C. for one hour and 280° C. for one hour to prepare a coating film A having a film thickness of about 100 ⁇ m. Further, film formation was carried out in the same manner, and the drying conditions were changed to 100° C. for one hour and 200° C. for one hour to prepare a coating film B. Further, using the polymer solution P1, film formation was carried out in the same manner as for the coating film B to prepare a coating film X. Then, a small-angle X-ray scattering measurement was carried out by using the above-mentioned coating films A, B and X by Nano-viewer manufactured by Rigaku Corporation. The measurement conditions were as shown below.
  • Length of camera 500 mm
  • IP imaging plate
  • Measurement mode transmission measurement
  • FIG. 5 The result of a small-angle X-ray ray scattering measurement of a cast film was shown in FIG. 5 .
  • the vertical axis represents the intensity (optional unit) of X-ray scattering
  • q of the horizontal axis represents a value of the following formula.
  • ⁇ is a wavelength
  • ⁇ is a scattering angle.
  • q 4 ⁇ / ⁇ sin( ⁇ /2)
  • A, B and X respectively represent scattering spectra of the coating films A, B and X.
  • Table 10 shows the temperature for the thermal treatment at the time of preparing the coating films A, B and X and the sizes (D) of the obtained non-uniform structures. From such results, it is estimated that a non-uniform portion of about 28 nm is present in the coating film A, and a non-uniform portion of about 20 nm is present in the coating film B.
  • Example or Comparative Example An electret in each Example or Comparative Example was prepared in the same manner as in Example 8 except that the polymer composition solution was changed to the polymer composition solution in Tables 11 and 12, and the temperature for the thermal treatment and the grid voltage were adjusted to the values in Tables 11 and 12.
  • Example or Comparative Example An electret in each Example or Comparative Example was prepared in the same manner as in Example 20 except that the polymer composition solution was changed to the polymer composition solution in Tables 13 and 14, and the temperature for the thermal treatment and the grid voltage were adjusted to the values in Tables 13 and 14.
  • the present invention is useful for the production of an electret which is used for an electrostatic induction conversion device such as a power-generating unit, a microphone, etc.
  • 10 copper substrate, 11 : coating film, 12 : DC high-voltage power source, 14 : corona needle, 16 : grid, 17 : ammeter, 18 : power source for grid, 19 : hotplate, 20 : counter electrode, 21 : electret, 22 : ammeter.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Compositions Of Macromolecular Compounds (AREA)
  • Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
  • Paints Or Removers (AREA)
  • Electrostatic, Electromagnetic, Magneto- Strictive, And Variable-Resistance Transducers (AREA)
  • Laminated Bodies (AREA)
US13/177,493 2009-02-20 2011-07-06 Process for producing electret, and electrostatic induction conversion device Expired - Fee Related US8288475B2 (en)

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JP2012085515A (ja) * 2010-09-16 2012-04-26 Murata Mfg Co Ltd エレクトレットの帯電装置及びエレクトレットの帯電方法、振動発電装置
KR101819780B1 (ko) 2010-12-03 2018-01-17 아사히 가라스 가부시키가이샤 전하 유지 매체의 제조 방법
TWI490901B (zh) * 2010-12-03 2015-07-01 Asahi Glass Co Ltd Charge to keep the media
CN102487468A (zh) * 2010-12-06 2012-06-06 洪爱琴 一种麦克风
JP2012137428A (ja) * 2010-12-27 2012-07-19 Asahi Glass Co Ltd 配管モニタリングシステム
CN102325293B (zh) * 2011-05-09 2014-01-22 东莞勤增实业有限公司 一种驻极体的极化装置及采用该极化装置进行极化的方法
EP2738781A4 (de) * 2011-07-28 2015-06-17 Asahi Glass Co Ltd Elektret und verfahren zu seiner herstellung sowie elektrostatisches induktionsumwandlungselement
WO2013157505A1 (ja) * 2012-04-17 2013-10-24 国立大学法人 埼玉大学 エレクトレット構体及びその製造方法並びに静電誘導型変換素子
EP4089121A4 (de) * 2020-01-08 2024-01-24 Daikin Industries, Ltd. Elektretmaterial und induktionsumwandlungselement
JPWO2023157589A1 (de) * 2022-02-21 2023-08-24

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US20110263788A1 (en) 2011-10-27
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JPWO2010095554A1 (ja) 2012-08-23
EP2400516A1 (de) 2011-12-28
CN102318021B (zh) 2013-09-25
TWI483622B (zh) 2015-05-01
WO2010095554A1 (ja) 2010-08-26
EP2400516B1 (de) 2016-06-08
KR20110116117A (ko) 2011-10-25
CN102318021A (zh) 2012-01-11
EP2400516A4 (de) 2014-11-26

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